It takes a generation to fix the negative effects of development restrictions. Apartment buildings typically go through a life cycle. They start out targeted at high-end residents, because that justifies the initial construction costs, then as they age get targeted down market. Chicago has a ton of reasonably affordable apartment housing, and most of it was built in the 1970's.

It will be decades before the shiny new buildings being put up new in San Francisco are affordable for ordinary people.